Method for reducing deposit formation in lubricant compositions

ABSTRACT

The deposit forming tendency of Group II, III and IV lubricating base oils is reduced by the use of synergistic mixtures of diphenylamines or phenyl-α-naphthylamines with triarylphosphites.

This application claims priority of Provisional Application 60/788,235filed Mar. 31, 2006.

FIELD OF THE INVENTION

The present invention relates to a method for reducing deposit formationin lubricant compositions. More particularly, the present inventionrelates to a synergistic combination of antioxidants that when added tolubricants reduce deposit formation in the lubricant.

BACKGROUND OF THE INVENTION

Modern lubricating compositions contain a major amount of an oil oflubricating viscosity and a minor amount of a plethora of performanceenhancing additives such as antioxidants, extreme pressure agents, pourpoint depressants, viscosity modifiers, and metal passivators to mentionjust a few.

Notwithstanding the development of numerous lubricating compositions tomeet specific equipment needs, current trends in equipment designrequire lubricants to function at higher temperatures and for longerperiods of time. Higher temperatures can lead to increased oxidation ofthe lubricating composition, thus stimulating the search forincreasingly improved antioxidants.

In Patent Publication U. S. 2003/0096713 A1, there is disclosed alubricating composition with improved oxidation resistance. Thelubricant contains at least 2 wt % of one or more antioxidants and adispersant or detergent. The antioxidants are selected from the groupconsisting of amine antioxidants, dithiophosphoric esters, phenolantioxidants, dithiocarbonates, aromatic phosphites, and sulfurizedfatty oils and olefins.

In Patent Publication U. S. 2003/0171227 A1 there is disclosedstabilizing compositions for lubricants that contain at least onediphenylamine and a neutral organophosphate or phosphite. Blends of theaminic antioxidant with certain phenolic antioxidants also aredisclosed. The stabilizing compositions are prepared by heating theantioxidants and phosphite for 0.2 to 6 hours at 40° C. to 150° C.

U.S. Pat. No. 6,172,014 B1 discloses a method for reducing compressorgas leakage by using a lubricant having at least one phosphiteantioxidant and at least one second antioxidant. The second antioxidantis selected from the group consisting of amine compounds, phenoliccompounds and mixtures thereof.

Although one might believe that improving the oxidation stability of alubricating composition should also result in reducing depositformation, experience has shown such is not always the case. Thus, thereremains a need for lubricant additives that will reduce depositformation in lubricating compositions.

SUMMARY OF THE INVENTION

Very simply, the present invention is based, in part, on the surprisingand unexpected discovery that reduced deposit formation in Group II, IIIand IV lubricating base oils can be achieved through the use ofsynergistic mixtures of diphenylamines or phenyl-α-naphthylamines withtriaryl phosphites.

Thus, in one aspect of the invention, a method is provided for reducingdeposit formation in lubricant base oils selected from the groupconsisting of Group II, III, IV and mixtures thereof by adding to thebase oils an effective amount of a mixture of diphenylamines orphenyl-α-naphthylamines with triaryl phosphites.

In another aspect, there is provided a lubricating compositioncomprising a major amount of an oil of lubricating viscosity selectedfrom the group consisting of Group II, III, IV and mixtures thereof anda minor but effective amount of a mixture of diphenylamines orphenyl-α-naphthylamines with triaryl phosphites.

The lubricating base oil suitable in the practice of the invention isany natural or synthetic oil selected from the group consisting ofGroups II, III, IV and mixtures thereof. Particularly preferred areGroup III base oils and especially GTL Group III base oils.

DETAILED DESCRIPTION OF THE INVENTION

GTL materials are materials that are derived via one or more synthesis,combination, transformation, rearrangement, and/ordegradation/deconstructive processes from gaseous carbon-containingcompounds, hydrogen-containing compounds, and/or elements as feedstockssuch as hydrogen, carbon dioxide, carbon monoxide, water, methane,ethane, ethylene, acetylene, propane, propylene, propyne, butane,butylenes, and butynes. GTL base stocks and base oils are GTL materialsof lubricating viscosity that are generally derived from hydrocarbons,for example waxy synthesized hydrocarbons, that are themselves derivedfrom simpler gaseous carbon-containing compounds, hydrogen-containingcompounds and/or elements as feedstocks. GTL base stock(s) include oilsboiling in the lube oil boiling range separated/fractionated from GTLmaterials such as by, for example, distillation or thermal diffusion,and subsequently subjected to well-known catalytic or solvent dewaxingprocesses to produce lube oils of reduced/low pour point; waxisomerates, comprising, for example, hydroisomerized or isodewaxedsynthesized hydrocarbons; hydroisomerized or isodewaxed Fischer-Tropsch(F-T) material (i.e., hydrocarbons, waxy hydrocarbons, waxes andpossible analogous oxygenates); preferably hydroisomerized or isodewaxedF-T hydrocarbons or hydroisomerized or isodewaxed F-T waxes,hydroisomerized or isodewaxed synthesized waxes, or mixtures thereof.

GTL base stock(s) derived from GTL materials, especially,hydroisomerized/isodewaxed F-T material derived base stock(s), and otherhydroisomerized/isodewaxed wax derived base stock(s) are characterizedtypically as having kinematic viscosities at 100° C. of from about 2mm²/s to about 50 mm²/s, preferably from about 3 mm²/s to about 50mm²/s, more preferably from about 3.5 mm²/s to about 30 mm²/s, asexemplified by a GTL base stock derived by the isodewaxing of F-T wax,which has a kinematic viscosity of about 4 mm²/s at 100° C. and aviscosity index of about 130 or greater. Reference herein to Kinematicviscosity refers to a measurement made by ASTM method D445.

GTL base stocks and base oils derived from GTL materials, especiallyhydroisomerized/isodewaxed F-T material derived base stock(s), and otherhydroisomerized/isodewaxed wax-derived base stock(s), such as waxhydroisomerates/isodewaxates, which are base stock components of thisinvention are further characterized typically as having pour points ofabout −5° C. or lower, preferably about −10° C. or lower, morepreferably about −15° C. or lower, still more preferably about −20° C.or lower, and under some conditions may have advantageous pour points ofabout −25° C. or lower, with useful pour points of about −30° C. toabout −40° C. or lower. If necessary, a separate dewaxing step may bepracticed to achieve the desired pour point. References herein to pourpoint refer to measurement made by ASTM D97 and similar automatedversions.

The GTL base stock(s) derived from GTL materials, especiallyhydroisomerized/isodewaxed F-T material derived base stock(s), and otherhydroisomerized/isodewaxed wax-derived base stock(s) which are basestock components of this invention are also characterized typically ashaving viscosity indices of 80 or greater, preferably 100 or greater,and more preferably 120 or greater. Additionally, in certain particularinstances, viscosity index of these base stocks may be preferably 130 orgreater, more preferably 135 or greater, and even more preferably 140 orgreater. For example, GTL base stock(s) that derive from GTL materialspreferably F-T materials especially F-T wax generally have a viscosityindex of 130 or greater. References herein to viscosity index refer toASTM method D2270.

In addition, the GTL base stock(s) are typically highly paraffinic (>90%saturates), and may contain mixtures of monocycloparaffins andmulticycloparaffins in combination with non-cyclic isoparaffins. Theratio of the naphthenic (i.e., cycloparaffin) content in suchcombinations varies with the catalyst and temperature used. Further, GTLbase stocks and base oils typically have very low sulfur and nitrogencontent, generally containing less than about 10 ppm, and more typicallyless than about 5 ppm of each of these elements. The sulfur and nitrogencontent of GTL base stock and base oil obtained by thehydroisomerization/isodewaxing of F-T material, especially F-T wax isessentially nil.

In a preferred embodiment, the GTL base stock(s) comprises paraffinicmaterials that consist predominantly of non-cyclic isoparaffins and onlyminor amounts of cycloparaffins. These GTL base stock(s) typicallycomprise paraffinic materials that consist of greater than 60 wt %non-cyclic isoparaffins, preferably greater than 80 wt % non-cyclicisoparaffins, more preferably greater than 85 wt % non-cyclicisoparaffins, and most preferably greater than 90 wt % non-cyclicisoparaffins.

Useful compositions of GTL base stock(s), hydroisomerized or isodewaxedF-T material derived base stock(s), and wax-derivedhydroisomerized/isodewaxed base stock(s), such as waxisomerates/isodewates, are recited in U.S. Pat. Nos. 6,080,301;6,090,989, and 6,165,949 for example.

Isomerate/isodewaxate base stock(s) derived from waxy feeds which arealso suitable for use in this invention, are paraffinic fluids oflubricating viscosity derived from hydroisomerized or isodewaxed waxyfeedstocks of mineral oil, non-mineral oil, non-petroleum, or naturalsource origin, e.g., feedstocks such as one or more of gas oils, slackwax, waxy fuels hydrocracker bottoms, hydrocarbon raffinates, naturalwaxes, hyrocrackates, thermal crackates, foots oil, wax from coalliquefaction or from shale oil, or other suitable mineral oil,non-mineral oil, non-petroleum, or natural source derived waxymaterials, linear or branched hydrocarbyl compounds with carbon numberof about 20 or greater, preferably about 30 or greater, and mixtures ofsuch isomerate/isodewaxate base stocks and base oils.

As used herein, the following terms have the indicated meanings:

-   -   (a) “wax”—hydrocarbonaceous material having a high pour point,        typically existing as a solid at room temperature, at about        15° C. to 25° C., and consisting predominantly of paraffinic        materials;    -   (b) “paraffinic” material: any saturated hydrocarbons, such as        alkanes. Paraffinic materials may include linear alkanes,        branched alkanes (iso-paraffins), cycloalkanes (cycloparaffins;        mono-ring and/or multi-ring), and branched cycloalkanes;    -   (c) “hydroprocessing”: a refining process in which a feedstock        is heated with hydrogen at high temperature and under pressure,        commonly in the presence of a catalyst, to remove and/or convert        less desirable components and to produce an improved product;    -   (d) “hydrotreating”: a catalytic hydrogenation process that        converts sulfur- and/or nitrogen-containing hydrocarbons into        hydrocarbon products with reduced sulfur and/or nitrogen        content, and which generates hydrogen sulfide and/or ammonia        (respectively) as byproducts; similarly, oxygen containing        hydrocarbons can also be reduced to hydrocarbons and water;    -   (e) “hydrodewaxing” (or catalytic dewaxing): a catalytic process        in which normal paraffins (wax) and/or waxy hydrocarbons are        converted by cracking/fragmentation into lower molecular weight        species, and by rearrangement/isomerization into more branched        iso-paraffins;    -   (f) “hydroisomerization” (or isomeriation or isodewaxing): a        catalytic process in which normal paraffins (wax) and/or        slightly branched iso-paraffins are converted by        rearrangement/isomerization into more branched iso-paraffins;    -   (g) “hydrocracking”: a catalytic process in which hydrogenation        accompanies the cracking/fragmentation of hydrocarbons, e.g.,        converting heavier hydrocarbons into lighter hydrocarbons, or        converting aromatics and/or cycloparaffins (naphthenes) into        non-cyclic branched paraffins.

As previously indicated, isomerate/isodewaxate base stock(s) suitablefor use as the necessary components in the present invention, can bederived from waxy feeds such as slack wax(es).

Slack wax is the wax recovered from petroleum oils by solvent orautorefrigerative dewaxing. Solvent dewaxing employs chilled solventsuch as methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK),mixtures of MEK/MIBK, mixtures of MEK and toluene, whileautorefrigerative dewaxing employs pressurized, liquefied low boilinghydrocarbons such as propane or butane.

Slack waxes, being secured from petroleum oils, may contain sulfur andnitrogen containing compounds. Such heteroatom compounds must be removedby hydrotreating (and not hydrocracking), as for example byhydrodesulfurization (HDS) and hydrodenitrogenation (HDN) so as to avoidsubsequent poisoning/deactivation of the hydroisomerization catalyst.

In a preferred embodiment, the GTL material, from which the GTL basestock(s) is/are derived is a F-T material (i.e., hydrocarbons, waxyhydrocarbons, wax). A slurry F-T synthesis process may be beneficiallyused for synthesizing the feed from CO and hydrogen and particularly oneemploying a F-T catalyst comprising a catalytic cobalt component toprovide a high alpha for producing the more desirable higher molecularweight paraffins. This process is also well known to those skilled inthe art.

In a F-T synthesis process, a synthesis gas comprising a mixture of H₂and CO is catalytically converted into hydrocarbons and preferablyliquid hydrocarbons. The mole ratio of the hydrogen to the carbonmonoxide may broadly range from about 0.5 to 4, but which is moretypically within the range of from about 0.7 to 2.75 and preferably fromabout 0.7 to 2.5. As is well known, F-T synthesis processes includeprocesses in which the catalyst is in the form of a fixed bed, afluidized bed or as a slurry of catalyst particles in a hydrocarbonslurry liquid. The stoichiometric mole ratio for a F-T synthesisreaction is 2.0, but there are many reasons for using other than astoichiometric ratio as those skilled in the art know. In a cobaltslurry hydrocarbon synthesis process the feed mole ratio of the H₂ to COis typically about 2.1/1. The synthesis gas comprising a mixture of H₂and CO is bubbled up into the bottom of the slurry and reacts in thepresence of the particulate F-T synthesis catalyst in the slurry liquidat conditions effective to form hydrocarbons, a portion of which areliquid at the reaction conditions and which comprise the hydrocarbonslurry liquid. The synthesized hydrocarbon liquid is separated from thecatalyst particles as filtrate by means such as filtration, althoughother separation means such as centrifugation can be used. Some of thesynthesized hydrocarbons pass out the top of the hydrocarbon synthesisreactor as vapor, along with unreacted synthesis gas and other gaseousreaction products. Some of these overhead hydrocarbon vapors aretypically condensed to liquid and combined with the hydrocarbon liquidfiltrate. Thus, the initial boiling point of the filtrate may varydepending on whether or not some of the condensed hydrocarbon vaporshave been combined with it. Slurry hydrocarbon synthesis processconditions vary somewhat depending on the catalyst and desired products.Typical conditions effective to form hydrocarbons comprising mostly C₅₊paraffins, (e.g., C₅₊-C₂₀₀) and preferably C₁₀₊ paraffins, in a slurryhydrocarbon synthesis process employing a catalyst comprising asupported cobalt component include, for example, temperatures, pressuresand hourly gas space velocities in the range of from about 320-850° F.,80-600 psi and 100-40,000 V/hr/V, expressed as standard volumes of thegaseous CO and H₂ mixture (0° C., 1 atm) per hour per volume ofcatalyst, respectively. It is preferred that the hydrocarbon synthesisreaction be conducted under conditions in which limited or no water gasshift reaction occurs and more preferably with no water gas shiftreaction occurring during the hydrocarbon synthesis. It is alsopreferred to conduct the reaction under conditions to achieve an alphaof at least 0.85, preferably at least 0.9 and more preferably at least0.92, so as to synthesize more of the more desirable higher molecularweight hydrocarbons. This has been achieved in a slurry process using acatalyst containing a catalytic cobalt component. Those skilled in theart know that by alpha is meant the Schultz-Flory kinetic alpha. Whilesuitable F-T reaction types of catalyst comprise, for example, one ormore Group VIII catalytic metals such as Fe, Ni, Co, Ru and Re, it ispreferred that the catalyst comprise a cobalt catalytic component. Inone embodiment the catalyst comprises catalytically effective amounts ofCo and one or more of Re, Ru, Fe, Ni, Th, Zr, Hf, U, Mg and La on asuitable inorganic support material, preferably one which comprises oneor more refractory metal oxides. Preferred supports for Co containingcatalysts comprise titania, particularly. Useful catalysts and theirpreparation are known and illustrative, but nonlimiting examples may befound, for example, in U.S. Pat. Nos. 4,568,663; 4,663,305; 4,542,122;4,621,072 and 5,545,674.

As set forth above, the waxy feed from which the base stock(s) is/arederived is wax or waxy feed from mineral oil, non-mineral oil,non-petroleum, or other natural source, especially slack wax, or GTLmaterial, preferably F-T material, referred to as F-T wax. F-T waxpreferably has an initial boiling point in the range of from 650-750° F.and preferably continuously boils up to an end point of at least 1050°F. A narrower cut waxy feed may also be used during thehydroisomerization. A portion of the n-paraffin waxy feed is convertedto lower boiling isoparaffinic material. Hence, there must be sufficientheavy n-paraffin material to yield an isoparaffin containing isomerateboiling in the lube oil range. If catalytic dewaxing is also practicedafter isomerization/isodewaxing, some of the isomerate/isodewaxate willalso be hydrocracked to lower boiling material during the conventionalcatalytic dewaxing. Hence, it is preferred that the end boiling point ofthe waxy feed be above 1050° F. (1050° F.+).

The waxy feed preferably comprises the entire 650-750° F.+ fractionformed by the hydrocarbon synthesis process, with the initial cut pointbetween 650° F. and 750° F. being determined by the practitioner and theend point, preferably above 1050° F., determined by the catalyst andprocess variables employed by the practitioner for the synthesis. Waxyfeeds may be processed as the entire fraction or as subsets of theentire fraction prepared by distillation or other separation techniques.The waxy feed also typically comprises more than 90%, generally morethan 95% and preferably more than 98 wt % paraffinic hydrocarbons, mostof which are normal paraffins. It has negligible amounts of sulfur andnitrogen compounds (e.g., less than 1 wppm of each), with less than2,000 wppm, preferably less than 1,000 wppm and more preferably lessthan 500 wppm of oxygen, in the form of oxygenates. Waxy feeds havingthese properties and useful in the process of the invention have beenmade using a slurry F-T process with a catalyst having a catalyticcobalt component, as previously indicated.

The process of making the lubricant oil base stocks from waxy stocks,e.g., slack wax or F-T wax, may be characterized as a hydrodewaxingprocess. If slack waxes are used as the feed, they may need to besubjected to a preliminary hydrotreating step under conditions alreadywell known to those skilled in the art to reduce (to levels that wouldeffectively avoid catalyst poisoning or deactivation) or to removesulfur- and nitrogen-containing compounds which would otherwisedeactivate the hydroisomerization/hydrodewaxing catalyst used insubsequent steps. If F-T waxes are used, such preliminary treatment isnot required because, as indicated above, such waxes have only traceamounts (less than about 10 ppm, or more typically less than about 5 ppmto nil) of sulfur or nitrogen compound content. However, somehydrodewaxing catalyst fed F-T waxes may benefit from removal ofoxygenates while others may benefit from oxygenates treatment. Thehydrodewaxing process may be conducted over a combination of catalysts,or over a single catalyst. Conversion temperatures range from about 150°C. to about 500° C. at pressures ranging from about 500 to 20,000 kPa.This process may be operated in the presence of hydrogen, and hydrogenpartial pressures range from about 600 to 6000 kPa. The ratio ofhydrogen to the hydrocarbon feedstock (hydrogen circulation rate)typically range from about 10 to 3500 n.l.l.⁻¹ (56 to 19,660 SCF/bbl)and the space velocity of the feedstock typically ranges from about 0.1to 20 LHSV, preferably 0.1 to 10 LHSV.

Following any needed hydridenitrogenation or hydrodesulfurization, thehydroprocessing used for the production of base stocks from such waxyfeeds may use an amorphous hydrocracking/hydroisomerization catalyst,such as a lube hydrocracking (LHDC) catalysts, for example catalystscontaining Co, Mo, Ni, W, Mo, etc., on oxide supports, e.g., alumina,silica, silica/alumina, or a crystallinehydrocracking/hydroisomerization catalyst, preferably a zeoliticcatalyst.

Other isomerization catalysts and processes forhydrocracking/hydroisomerized/isodewaxing GTL materials and/or waxymaterials to base stock or base oil are described, for example, in U.S.Pat. Nos. 2,817,693; 4,900,407; 4,937,399; 4,975,177; 4,921,594;5,059,299; 5,200,382; 5,516,740; 5,182,248; 5,290,426; 5,580,442;5,976,351; 5,935,417; 5,885,438; 5,965,475; 6,190,532;6,375,830;6,332,974; 6,103,099; 6,025,305; 6,080,301; 6,096,940; 6,620,312;6,676,827; 6,383,366; 6,475,960; 5,059,299; 5,977,425; 5,935,416;4,923,588; 5,158,671; and 4,897,178; EP 0324528 (B1), EP 0532116 (B1),EP 0532118 (B1), EP 0537815 (B1), EP 0583836 (B2), EP 0666894 (B2), EP0668342 (B1), EP 0776959 (A3), WO 97/031693 (A1), WO 02/064710 (A2), WO02/064711 (A1), WO 02/070627 (A2), WO 02/070629 (A1), WO 03/033320 (A1)as well as in British Patents 1,429,494; 1,350,257; 1,440,230;1,390,359; WO 99/45085 and WO 99/20720. Particularly favorable processesare described in European Patent Applications 464546 and 464547.Processes using F-T wax feeds are described in U.S. Pat. Nos. 4,594,172;4,943,672; 6,046,940; 6,475,960; 6,103,099; 6,332,974; and 6,375,830.

Hydrocarbon conversion catalysts useful in the conversion of then-paraffin waxy feedstocks disclosed herein to form the isoparaffinichydrocarbon base oil are zeolite catalysts, such as ZSM-5, ZSM-11,ZSM-23, ZSM-35, ZSM-12, ZSM-38, ZSM-48, offretite, ferrierite, zeolitebeta, zeolite theta, zeolite alpha, as disclosed in U.S. Pat. No.4,906,350. These catalysts are used in combination with Group VIIImetals, in particular palladium or platinum. The Group VIII metals maybe incorporated into the zeolite catalysts by conventional techniques,such as ion exchange.

In one embodiment, conversion of the waxy feedstock may be conductedover a combination of Pt/zeolite beta and Pt/ZSM-23 catalysts in thepresence of hydrogen. In another embodiment, the process of producingthe lubricant oil base stocks comprises hydroisomerization and dewaxingover a single catalyst, such as Pt/ZSM-35. In yet another embodiment,the way feed can be fed over Group VIII metal loaded ZSM-48, preferablyGroup VIII noble metal loaded ZSM-48, more preferably Pt/ZSM-48 ineither one stage or two stages. In any case, useful hydrocarbon base oilproducts may be obtained. Catalyst ZSM-48 is described in U.S. Pat. No.5,075,269, the disclosure of which is incorporated herein by referencein its entirety. The use of the Group VIII metal loaded ZSM-48 family ofcatalysts in the isodewaxing of the waxy feedstock eliminates the needfor any subsequent, separate dewaxing step, and is preferred.

A dewaxing step, when needed, may be accomplished using either wellknown solvent or catalytic dewaxing processes and either the entirehydroisomerate or the 650-750° F.+ fraction may be dewaxed, depending onthe intended use of the 650-750° F.− material present, if it has notbeen separated from the higher boiling material prior to the dewaxing.In solvent dewaxing, the hydroisomerate may be contacted with chilledsolvents such as acetone, methyl ethyl ketone (MEK), methyl isobutylketone (MIBK), mixtures of MEK/MIBK, or mixtures of MEK/toluene and thelike, and further chilled to precipitate out the higher pour pointmaterial as a waxy solid which is then separated from thesolvent-containing lube oil fraction which is the raffinate. Theraffinate is typically further chilled in scraped surface chillers toremove more wax solids. Low molecular weight hydrocarbons, such aspropane, are also used for dewaxing, in which the hydroisomerate ismixed with liquid propane, a least a portion of which is flashed off tochill down the hydroisomerate to precipitate out the wax. The wax isseparated from the raffinate by filtration, membrane separation orcentrifugation. The solvent is then stripped out of the raffinate, whichis then fractionated to produce the preferred base stocks useful in thepresent invention. Also well known is catalytic dewaxing, in which thehydroisomerate is reacted with hydrogen in the presence of a suitabledewaxing catalyst at conditions effective to lower the pour point of thehydroisomerate. Catalytic dewaxing also converts a portion of thehydroisomerate to lower boiling materials, in the boiling range, forexample, 650-750° F.−, which are separated from the heavier 650-750° F.+base stock fraction and the base stock fraction fractionated into two ormore base stocks. Separation of the lower boiling material may beaccomplished either prior to or during fraction of the 650-750° F.+material into the desired base stocks.

Any dewaxing catalyst which will reduce the pour point of thehydroisomerate and preferably those which provide a large yield of lubeoil base stock from the hydroisomerate may be used. These include shapeselective molecular sieves which, when combined with at least onecatalytic metal component, have been demonstrated as useful for dewaxingpetroleum oil fractions and include, for example, ferrierite, mordenite,ZSM-5, ZSM-11, ZSM-23, ZSM-35, ZSM-22 also known as theta one or TON,and the silicoaluminophosphates known as SAPO's. A dewaxing catalystwhich has been found to be unexpectedly particularly effective comprisesa noble metal, preferably Pt, composited with H-mordenite. The dewaxingmay be accomplished with the catalyst in a fixed, fluid or slurry bed.Typical dewaxing conditions include a temperature in the range of fromabout 400-600° F., a pressure of 500-900 psig, H₂ treat rate of1500-3500 SCF/B for flow-through reactors and LHSV of 0.1-10, preferably0.2-2.0. The dewaxing is typically conducted to convert no more than 40wt % and preferably no more than 30 wt % of the hydroisomerate having aninitial boiling point in the range of 650-750° F. to material boilingbelow its initial boiling point.

GTL base stock(s), isomerized or isodewaxed wax-derived base stock(s),have a beneficial kinematic viscosity advantage over conventional GroupII and Group III base stocks and base oils, and so may be veryadvantageously used with the instant invention. Such GTL base stocks andbase oils can have significantly higher kinematic viscosities, up toabout 20-50 mm²/s at 100° C., whereas by comparison commercial Group IIbase oils can have kinematic viscosities, up to about 15 mm²/s at 100°C., and commercial Group III base oils can have kinematic viscosities,up to about 10 mm²/s at 100° C. The higher kinematic viscosity range ofGTL base stocks and base oils, compared to the more limited kinematicviscosity range of Group II and Group III base stocks and base oils, incombination with the instant invention can provide additional beneficialadvantages in formulating lubricant compositions.

In the present invention the one or more isomerate/isodewaxate basestock(s), the GTL base stock(s), or mixtures thereof, preferably GTLbase stock(s) can constitute all or part of the base oil.

The preferred base stock(s) derived from GTL materials and/or from waxyfeeds is/are are characterized as having predominantly paraffiniccompositions and are further characterized as having high saturateslevels, low-to-nil sulfur, low-to-nil nitrogen, low-to-nil aromatics,and are essentially water-white in color.

The one or more isomerate/isodewaxate base stock(s), GTL base stock(s),or mixtures thereof, preferably GTL base stock(s) can constitute from 5to 100%, preferably 40 to 100%, more preferably 70 to 100% by weight ofthe total of the base oil, the amount employed being left to thepractitioner in response to the requirements of the finished lubricant.

In addition to the one or more hydroisomerized/isodewaxate basestock(s), GTL base stock(s), or mixtures thereof, preferably GTL basestock(s) which is/are an essential, necessary component to achieve theunexpected improvement in both the initial and long term metal corrosionresistance, the base oil can contain natural oils as well as othersynthetic oils and non-conventional oils and mixtures thereof.

Natural oil, other synthetic oils, and unconventional oils and mixturesthereof can be used unrefined, refined, or rerefined (the latter is alsoknown as reclaimed or reprocessed oil). Unrefined oils are thoseobtained directly from a natural, synthetic or unconventional source andused without further purification. These include for example shale oilobtained directly from retorting operations, oils derived from coal,petroleum oil obtained directly from primary distillation, and ester oilobtained directly from an esterification process. Refined oils aresimilar to the oils discussed for unrefined oils except refined oils aresubjected to one or more purification or transformation steps to improveat least one lubricating oil property. One skilled in the art isfamiliar with many purification or transformation processes. Theseprocesses include, for example, solvent extraction, secondarydistillation, acid extraction, base extraction, filtration, percolation,hydrogenation, hydrorefining, and hydrofinishing. Rerefined oils areobtained by processes analogous to refined oils, but use an oil that hasbeen previously used.

Groups I, II, III, IV and V are broad categories of base oil stocksdeveloped and defined by the American Petroleum Institute (APIPublication 1509; www.API.org) to create guidelines for lubricant baseoils. Group I base stocks generally have a viscosity index of betweenabout 80 to 120 and contain greater than about 0.03% sulfur and lessthan about 90% saturates. Group II base stocks generally have aviscosity index of between about 80 to 120, and contain less than orequal to about 0.03% sulfur and greater than or equal to about 90%saturates. Group III stock generally has a viscosity index greater thanabout 120 and contains less than or equal to about 0.03% sulfur andgreater than about 90% saturates. Group IV includes polyalphaolefins(PAO). Group V base stocks include base stocks not included in GroupsI-IV. Table A summarizes properties of each of these five groups.

TABLE A Base Stock Properties Saturates Sulfur Viscosity Index Group I<90% and/or >0.03% and ≧80 and <120 Group II ≧90% and ≦0.03% and ≧80 and<120 Group III ≧90% and ≦0.03% and ≧120 Group IV Polyalphaolefins (PAO)Group V All other base oil stocks not included in Groups I, II, III, orIV

Natural oils include animal oils, vegetable oils (castor oil and lardoil, for example), and mineral oils. Animal and vegetable oilspossessing favorable thermal oxidative stability can be used. Of thenatural oils, mineral oils are preferred. Mineral oils vary widely as totheir crude source, for example, as to whether they are paraffinic,naphthenic, or mixed paraffinic-naphthenic. Oils derived from coal orshale are also useful in the present invention. Natural oils vary alsoas to the method used for their production and purification, forexample, their distillation range and whether they are straight run orcracked, hydrorefined, or solvent extracted.

Synthetic oils include hydrocarbon oils as well as non hydrocarbon oils.Synthetic oils can be derived from processes such as chemicalcombination (for example, polymerization, oligomerization, condensation,alkylation, acylation, etc.), where materials consisting of smaller,simpler molecular species are built up (i.e., synthesized) intomaterials consisting of larger, more complex molecular species.Synthetic oils include hydrocarbon oils such as polymerized andinterpolymerized olefins (polybutylenes, polypropylenes, propyleneisobutylene copolymers, ethylene-olefin copolymers, andethylene-alphaolefin copolymers, for example). Polyalphaolefin (PAO) oilbase stock is a commonly used synthetic hydrocarbon oil. By way ofexample, PAO's derived from C₈, C₁₀, C₁₂, C₁₄ olefins or mixturesthereof may be utilized. See U.S. Pat. Nos. 4,956,122; 4,827,064; and4,827,073.

The number average molecular weights of the PAO's, which are knownmaterials and generally available on a major commercial scale fromsuppliers such as ExxonMobil Chemical Company, Chevron, BP-Amoco, andothers, typically vary from about 250 to about 3000, or higher, andPAO's may be made in viscosities up to about 100 mm²/s (100° C.), orhigher. In addition, higher viscosity PAO's are commercially available,and may be made in viscosities up to about 3000 mm²/s (100° C.), orhigher. The PAO's are typically comprised of relatively low molecularweight hydrogenated polymers or oligomers of alpha-olefins whichinclude, but are not limited to, about C₂ to about C₃₂ alphaolefins withabout C₈ to about C₁₆ alphaolefins, such as 1-octene, 1-decene,1-dodecene and the like, being preferred. The preferred polyalphaolefinsare poly-1-octene, poly-1-decene and poly-1-dodecene and mixturesthereof and mixed olefin-derived polyolefins. However, the dimers ofhigher olefins in the range of about C₁₄ to C₁₈ may be used to providelow viscosity base stocks of acceptably low volatility. Depending on theviscosity grade and the starting oligomer, the PAO's may bepredominantly trimers and tetramers of the starting olefins, with minoramounts of the higher oligomers, having a viscosity range of about 1.5to 12 mm²/s.

PAO fluids may be conveniently made by the polymerization of analphaolefin in the presence of a polymerization catalyst such as theFriedel-Crafts catalysts including, for example, aluminum trichloride,boron trifluoride or complexes of boron trifluoride with water, alcoholssuch as ethanol, propanol or butanol, carboxylic acids or esters such asethyl acetate or ethyl propionate. For example the methods disclosed byU.S. Pat. No. 4,149,178 or U.S. Pat. No. 3,382,291 may be convenientlyused herein. Other descriptions of PAO synthesis are found in thefollowing U.S. Pat. Nos. 3,742,082; 3,769,363; 3,876,720; 4,239,930;4,367,352; 4,413,156; 4,434,408; 4,910,355; 4,956,122; and 5,068,487.The dimers of the C₁₄ to C₁₈ olefins are described in U.S. Pat. No.4,218,330.

Other useful synthetic lubricating base stock oils such as silicon-basedoil or esters of phosphorus containing acids may also be utilized. Forexamples of other synthetic lubricating base stocks are the seminal work“Synthetic Lubricants”, Gunderson and Hart, Reinhold Publ. Corp., NY1962.

In the practice of the invention, the deposit reducing additivecomprises a mixture of triaryl phosphites represented by Formula I withdiphenylamines or phenyl-α-naphthylamines represented by Formula II andIII respectively.

wherein R₁ is H or a hydrocarbyl group having from 1 to about 8 carbonatoms and R₂ is H or a hydrocarbyl group of from 1 to about 12 carbonatoms and R₃ is a hydrocarbyl group of from 1 to 12 carbon atoms or NHR₄where R₄ is a hydrocarbyl group of from 1 to about 12 carbon atoms.Preferably R₁ is tert-butyl, R₂ is H and R₃ is octyl

In the practice of the invention, the weight ratio of the diphenylamineor phenyl-α-naphthylamine to alkylated triaryl phosphite used willgenerally be in the range of from about 5:1 to about 1:5 and preferablyabout 2:1 to about 1:2.

Typically, the deposit reducing additive will be added to thelubricating base oil in the range of from about 0.1 wt % to about 2.0 wt%, and preferably from about 0.4 wt % to about 1.0 wt %, based on thetotal weight of the composition.

A lubricating oil composition of the invention comprises the majoramount of an oil of lubricating viscosity selected from the groupconsisting of Group II, III, IV and mixtures thereof and a minor amountof the deposit-reducing additive mixture of the invention.

The lubricating composition may be formulated with one or moreadditional additives such as pour point depressants, rust inhibitors,metal passivators, VI improvers, extreme pressure additives,demulsifiers, dispersants, solubilizers, antifoamants and dyes.

EXAMPLES

In the formulations presented in Tables 2 and 3, Irganox L06 isoctylphenyl-α-naphthylamine sold by Ciba-Geigy and Irgafos 168 isalkylated triaryl phosphite also sold by Ciba-Geigy.

The formulated oils were subjected to the performance tests listed inthe Tables along with the results of those tests. In the Tables, RPVOTrefers to the Rotary Pressure Vessel Oxidation Test (ASTM D2272). TheHot Tube Test is a test designed to simulate actual engine conditions. Arating of 10 in the test indicates heavy deposits, while a rating of 0indicates no discernable deposit.

Example 1 and Comparative Examples 1 to 4

A series of oils was prepared having the composition and propertiesshown in Table 2:

TABLE 2 Comparative 1 Example 1 Comparative 2 Comparative 3 Comparative4 Component, wt % Irganox 106 0.3 0.3 0.6 0.3 Irgafos 168 0.3 0.3 0.6Rust inhibitor 0.1 0.1 0.1 0.1 0.1 Triphenyl phosphate 0.3 Metaldeactivator 0.01 0.01 0.01 0.01 0.01 Defoamant 0.1 0.1 0.1 0.1 0.1 GroupI oil 99.19 Group II oil (1) 99.19 99.19 99.19 99.19 Properties Hot tubetest, 250° C. 7/6 2/2 9/10 10/10 Hot tube test, 270° C. 9 9 9.5 9 9RPVOT, mins 586 2520 2067 221 1280 (1) = JURONG 150

This data illustrates the synergistic and deposit reducing effect of theadditive mixture of the invention. The data also illustrates that theoxidation stability of an oil is not indicative of its deposit formingtendency. Note that Comparative Oil 2 had a relatively high oxidationstability test result but also had a very high deposit test result.

Examples 2 to 5 and Comparative Examples 5 to 8

Another series of oils was prepared. Their compositions and propertiesare given in Table 3.

TABLE 3 Example 2 Example 3 Example 4 Comparative 5 Comparative 6Comparative 7 Comparative 8 Component, wt % Irganox 106 0.3 0.3 0.3 0.30.3 0.6 Irgafos 168 0.3 0.3 0.3 0.6 Rust inhibitor 0.1 0.1 0.1 0.1 0.10.1 0.1 Triphenylphosphate 0.3 0.3 Metal deactivator 0.01 0.01 0.01 0.010.01 0.01 0.01 Defoamant 0.1 0.1 0.1 0.1 0.1 0.1 0.1 Group III (2) 99.19Group III (GTL) 99.19 99.19 99.19 99.19 Group III (3) 99.19 99.19Properties Hot tube test, 250° C. 2.5 2 — — — — — Hot tube test, 270° C.6.5 4 9 9 3/3 3 4 RBOT, mins 2870 2506 2067 1672 2792 2830 548 (2) =VISOM (3) = YUBASE

As can be seen, the additive mixture of the invention has a beneficialeffect on the deposit forming tendencies of the Group III and IVlubricant compositions. The data also shows that the mixture ofadditives of the invention results in significantly less deposits formedwhen used in a GTL base oil as compared to other Group III base oils.

1. A method for reducing deposit formation in a lubricating base oilselected from the group consisting of Group II, III, IV oils andmixtures thereof comprising adding to the oil an effective amount of amixture of triaryl phosphites represented by Formula I withdiphenylamines or phenyl-α-naphthylamines represented by Formula II andIII respectively,

wherein R₁ is H or a hydrocarbyl group having from 1 to about 8 carbonatoms and R₂ is H or a hydrocarbyl group of from 1 to about 12 carbonatoms and R₃ is a hydrocarbyl group of from 1 to 12 carbon atoms or NHR₄where R₄ is a hydrocarbyl group of from 1 to about 12 carbon atoms. 2.The method of claim 1 wherein the weight ratio of diphenylamine orphenyl-α-naphthylamine to the triaryl phosphite in the mixture is in therange of from about 5:1 to about 1:5.
 3. The method of claim 2 whereinthe amount of the mixture added to the base oil is in the range of about0.1 wt % to about 2 wt % based on the total weight of the composition.4. The method of claim 3 wherein R₁ is tert-butyl, R₂ is H and R₃ isoctyl.
 5. The method of claim 4 wherein the oil is a Group III oil. 6.The method of claim 5 wherein the Group III oil is a GTL oil.
 7. Alubricating composition having reduced deposit forming tendency asevidenced by the Hot Tube Test, comprising: a major amount of an oil oflubricating viscosity selected from the group consisting of Group II,III, IV oils and mixtures thereof; and a minor amount of a mixture oftriaryl phosphites represented by Formula I with diphenylamines orphenyl-α-naphthylamines represented by Formula II and III respectively.

wherein R₁ is H or a hydrocarbyl group having from 1 to about 8 carbonatoms and R₂ is H or a hydrocarbyl group of from 1 to about 12 carbonatoms and R₃ is a hydrocarbyl group of from 1 to 12 carbon atoms or NHR₄where R₄ is a hydrocarbyl group of from 1 to about 12 carbon atoms. 8.The composition of claim 7 wherein the weight ratio of diphenylamine orphenyl-α-naphthylamine to triaryl phosphite in the mixture is in therange of from about 5:1 to about 1:5.
 9. The composition of claim 8wherein the amount of the mixture is in the range of from about 0.1 wt %to about 2 wt %, based on the total weight of the composition.
 10. Thecomposition of claim 9 wherein R₁ is tert-butyl, R₂ is H and R₃ isoctyl.
 11. The composition of claim 10 wherein the base oil is a GroupIII base oil.
 12. The composition of claim 11 wherein the Group III baseoil is a GTL oil.
 13. A method for reducing deposit formation in alubricating base oil selected from the group consisting of Group II,III, IV oils and mixtures thereof comprising adding to the oil aneffective amount of a mixture of triaryl phosphites represented byFormula I with diphenylamines or phenyl-α-naphthylamines represented byFormula II and III respectively,

wherein R₁ is H or a hydrocarbyl group having from 1 to about 8 carbonatoms and R₂ is H or a hydrocarbyl group of from 1 to about 12 carbonatoms and R₃ is a hydrocarbyl group of from 1 to 12 carbon atoms or NHR₄where R₄ is a hydrocarbyl group of from 1 to about 12 carbon atoms andwherein the weight ratio of diphenylamines or phenyl-α-naphthylamines totriaryl phosphites is in the range of about 5:1 to about 1:5.